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:''This article is an overview of the subject. For a more technical discussion and for information related to current research, see Entropy (arrow of time).'' The Arrow of Time, or Time's Arrow, is a concept developed in 1927 by the British astronomer Arthur Eddington involving the "one-way direction" or "asymmetry" of time. This direction, according to Eddington, can be determined by studying the organization of atoms, molecules, and bodies, might be drawn upon a four-dimensional relativistic map of the world (''"a solid block of paper"'').〔, (Chapter 4, p. 143 ) 〕 Physical processes at the microscopic level are believed to be either entirely or mostly time-symmetric: if the direction of time were to reverse, the theoretical statements that describe them would remain true. Yet at the macroscopic level it often appears that this is not the case: there is an obvious direction (or ''flow'') of time. ==Eddington== In the 1928 book ''The Nature of the Physical World'', which helped to popularize the concept, Eddington stated: Let us draw an arrow arbitrarily. If as we follow the arrow we find more and more of the random element in the state of the world, then the arrow is pointing towards the future; if the random element decreases the arrow points towards the past. That is the only distinction known to physics. This follows at once if our fundamental contention is admitted that the introduction of randomness is the only thing which cannot be undone. I shall use the phrase ‘time's arrow’ to express this one-way property of time which has no analogue in space. Eddington then gives three points to note about this arrow: #It is vividly recognized by consciousness. #It is equally insisted on by our reasoning faculty, which tells us that a reversal of the arrow would render the external world nonsensical. #It makes no appearance in physical science except in the study of organization of a number of individuals. According to Eddington the arrow indicates the direction of progressive increase of the random element. Following a lengthy argument upon the nature of thermodynamics he concludes that, so far as physics is concerned, time's arrow is a property of entropy alone. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「arrow of time」の詳細全文を読む スポンサード リンク
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